Archive for January, 2007

A sgraffito technique can be used very effectively in enamel work, especially since it is difficult to achieve a line design with enamels without resorting to overglazes. A base coat of transparent or opaque enamel is applied and fired. This will be the color of the line design. Opaque enamels are then dusted over the piece in a design pattern. For example, if the design is to be a flower, the color chosen for the flower should be dusted in approximately the area where the flower is to be scratched, the color of the leaves then dusted in their approximate area, etc. Naturally, the design will look somewhat vague at this point, as it is nothing more than a color pattern. Shake off the excess enamel before starting any sgraffito work; too much enamel will render the scratching difficult. Using the colors as your guide, scratch the design through the enamel with a very sharp pencil, blowing away any loose particles of

Illustration 147
Sgraffito on enamel is very effective. First apply a coat of gum solution.

Illustration 148
148. Dark blue enamel is dusted over the entire piece.

Illustration 149
149. After firing, gum is re-applied and white, red-brown and turquoise enamels are dusted on in a general design pattern.

Illustration 150
150. The design is drawn through the dusted enamel with a very sharp pencil and the enamel is fired again.

Illustration 151
A few accents of wet charge are added and the enamel is fired for the final time. The line design should he kept very simple.

enamel that may clog the lines in the process. Keep the line design free and fairly simple. After the piece has been fired, accents can be added or colors made stronger as long as the original lines are scratched through again. By dusting another color over parts of the fired design, sgraffito lines of a second color can be produced. (See Appendix.)

Keywords: Ceramic Decorations, Ceramics Decor, Ceramics, Painting

Firing

Enamels may be fired in a special copper enameling kiln or in a ceramic kiln that opens from the front. Unlike ceramic firing which is slow firing from cool to hot to cool again, enamels are fired rapidly in a preheated kiln (1400 -1500 ) and removed at the same temperature.

The enamel must be completely dry before it is placed in the kiln. Place the dry piece on a stainless steel stand and transfer it to the preheated kiln with a spatula, wire tongs or a rack fork. The firing should be from two to four minutes. Experience will help you determine the correct length of time for various enamels.

The transparents usually require a slightly higher firing than most of the opaques and if the transparent enamel remains opaque after firing, it probably should be fired again at a higher temperature. A perfectly fired piece will be smooth and glassy; a pebbly, orange-skin surface means that the piece is underfired. It can be refired as it is or a design can be added and the piece then fired again.

Many copper enameling kilns are designed to permit the enamelist to watch the piece as it is being fired, but with the ceramic kilns a pyrometer is almost a necessity for controlling the temperature, especially with the more advanced techniques of enameling where a slight variation of temperature can be disastrous. Remove the piece from the kiln while it is red hot, if the surface appears smooth and shiny, and allow it to cool gradually. You will notice as the piece cools that tiny black flakes of fire scale oxidized metal which forms on the exposed copper area-will fly off the piece. Be careful that these specks of fire scale do not land in the enamel for they will fire onto it immediately. Commercial preparations are available that may be applied to the copper areas before firing to help prevent fire scale.

To prevent warping, it is a good idea to allow the enameled piece to cool on an asbestos board with a heavy weight on top of it. Another common enameling problem is the cracking of the enamel after it has been fired and cooled. This is caused by uneven expansion of the enamel and the copper and can generally be avoided by enameling both sides of the copper piece, a process called counterenameling. Unless there has been an overly heavy application of enamel, it is usually unnecessary to counterenamel concave pieces, such as dishes, ash trays, etc., but on flat or convex surfaces it should be used as a safeguard against cracking.

Illustration 146
Enamels are fired rapidly in a preheated kiln. Firing takes from two to four minutes, and the piece is removed while the kiln is still hot.

Keywords: Ceramic Decorations, Ceramics Decor, Ceramics, Painting

The ceramist will find applying enamels quite different from ceramic colors since enamels (with the exception of the over-glazes) are not mixed and painted on with a brush in the usual way.

One way to apply enamels is to dust or sift the dry color. The clean copper piece is first given a coat of gum tragacanth or the special preparation, applied with a brush or sprayed with an atomizer. This will hold the fine particles of enamel in place. Then a base coat of transparent or opaque enamel is sifted on the piece through an 80 mesh wire screen (a piece of nylon stocking can be used instead or you can obtain from enamel dealers and manufacturers special jar lids that are already fitted with a small piece of 80 mesh screen). Before dusting on the enamel, place a clean sheet of paper under the piece to catch the excess enamel so that it can be returned to the jar.

When you are certain that the piece has been well covered, shake off the excess enamel by tapping the piece on its side. With most transparent enamels, especially the brown, yellow and beige shades, one thin coat is usually sufficient as a heavy coat will destroy the transparency. However, the transparent greens and blues, because they are affected by the warm copper tone, generally require a heavier application or a second coat to achieve the full intensity of color. With the opaque enamels you may find it necessary after firing the first coat to apply a second coat; opaque reds in particular, when applied directly on copper, tend to burn out and a clear red can seldom be achieved with one coat.

Another way to apply enamels is to inlay the wet colors, a method referred to as wet charging. This can be done directly on the copper or over a fired coat of flux (clear transparent enamel), which is actually more satisfactory. The advantage of the wet charge method is that transparent enamels can be placed next to opaque enamels and it is also the best way to execute a design consisting of

Illustration 145
The copper tie bars are decorated with wet charge on a fired enamel base coat.

complex shapes and numerous color areas. For the inlaying method, a small amount of gum is added to the dry enamel until a thick paste is formed. Do not allow the paste to become too fluid or it will be difficult to control. With a spatula or brush, place the enamel in position on the copper piece and push the wet enamel into the desired shape (a fine brush is excellent for pushing the enamel). Level the enamel with a spreader or brush and inlay the next color, continuing the procedure until the entire surface is covered and the color areas joined. Tap the piece gently on the side to level the enamels.

Keywords: Ceramic Decorations, Ceramics Decor, Ceramics, Painting

Preparing the copper

Although silver and steel are also used for enameling, copper is by far the most practical metal. The all-important factor in the

Illustration 144
To clean copper, immerse it in an acid solution with tongs.

preparation of the copper is cleanliness, for the enamel will not adhere to a metal surface on which there is the slightest trace of grease or dirt.

There are several methods that can be used to clean the copper, one of which is the acid bath. The usual acid solution consists of one part nitric acid added to five parts water. Be sure to add the acid to the water. Never add water to acid or a violent chemical reaction will result, causing serious burns to anything with which the acid solution conies in contact. When preparing the solution, place the water in a glass dish and slowly add the nitric acid. Immerse the copper piece in the solution with tongs and remove the piece when the copper is a clean, pink color. Rinse and dry the copper immediately. Test the copper for cleanliness by running water over it. If the water does not form beads, the copper is ready to be enameled.

If it is not practical to work with acids, other methods may be used. One way to clean the copper without using an acid bath is by means of a commercial preparation which is a non-hazardous granular compound that is mixed with water. The copper piece is placed in the solution until clean. Another way to clean the copper is to rub the surface with steel wool and scouring powder or a clean rag that has been soaked in vinegar and dipped in salt.

While any of the foregoing methods are satisfactory and are the generally accepted cleaning methods, some arts and crafts stores now have a specially prepared gum solution that can be used instead. With it no cleaning is necessary except a polishing of the copper with steel wool or a copper cleaner to remove oxidation stains. You apply the preparation to the polished copper surface with a brush and it acts as a cleaning agent and also as the adhesive for dusting on the enamel. It can be used only when a coat of enamel is to be dusted on, not when a wet charge method is used.

Keywords: Ceramic Decorations, Ceramics Decor, Ceramics, Painting

Copper enameling

Have you ever thought of exploring another fascinating field closely allied to ceramics, that of copper enameling? Since enamels and ceramic glazes are both a form of glass and both are fired at high temperatures in a kiln, it is not surprising that so many ceramists include enameling in their ceramic activities. Naturally we do not intend to cover the entire field of copper enameling in one chapter, but it is hoped that the information offered here may inspire you to pursue the subject further.

Types of enamels

Glass enamels are generally purchased in ground form. When applied to metal and heated they fuse to a glassy coating, much like a ceramic glaze. There are four types of enamels available to the enamelist: opaque, transparent, opalescent, and overglaze enamels. Opaque enamels are solid colors through which light will not pass; transparent enamels permit the surface of the metal to be seen through the colors; opalescent enamels are transparents with a milky appearance; and the overglazes are used for detail work over an enameled surface. For general purposes, the opaque and transparent enamels are quite adequate and provide the enamelist with a wide range of colors and effects.

One of the main differences between enamels and ceramic glazes is that the enamels cannot be mixed to produce new shades of color. Unfortunately, when two enamels are mixed the tiny grains of each color will show up as specks rather than as a smooth new color. For this reason, the enamelist requires a large palette of colors.

Keywords: Ceramic Decorations, Ceramics Decor, Ceramics, Painting